The present invention relates to a novel and improved pressure sensitive resistor element.
There are known various types of pressure sensitive resistor elements having different mechanisms for pressure sensitiveness. A typical prior art pressure sensitive resistor element comprises a sheet of an electrically insulating rubbery material as a matrix, a number of electroconductive fibers dispersed in the matrix and oriented in alignment in a direction parallel to the thickness of the sheet, and electrodes provided on both surfaces of the sheet in electric contact. In order to obtain pressure sensitiveness in this type of resistor elements, it is essential that at least part of the electroconductive fibers do not penetrate the sheet from one surface to the other, so that the application of a compressive force between the electrodes brings about decreases in the thickness of the sheet whereby the number of the fibers reaching both surfaces of the sheet increases gradually as the compressive force is increased.
The pressure sensitive resistor elements not only of this type but also of other types have a problem that they exhibit some electric conduction even when no compressive force is applied and cannot be an electric insulator even in the absence of a compressive force. Therefore, it is a common practice that an on-off switching device is provided in series with the pressure sensitive resistor element in order to open the electric circuit. Further, inconvenience and inefficiency have been unavoidable in the assembling of the electric circuit, while sufficient miniaturization of the components cannot be achieved due to the necessity of a separate switching device.